Pneumatic Symbols

Compressor

Circle with an open triangle pointing to the outlet and a drive shaft, representing the machine that compresses atmospheric air. It starts the air supply section of a pneumatic diagram.

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Air receiver

Horizontal capsule for the pressure vessel that stores compressed air and evens out demand peaks. Drawn between the compressor and the distribution network.

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Pneumatic pressure source

Small circle with an open triangle that stands for the compressed air supply without detailing the compressor plant. Use it at the supply port of machine-level circuits.

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Air filter with manual drain

Square on its corner with a dashed filter element, a condensate bowl and a manual drain at the bottom. It removes particles and water before the air reaches valves and cylinders.

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Pressure regulator, relieving

Adjustable regulator that keeps outlet pressure, sensed through the dashed line, at the spring setting and vents excess downstream pressure through its exhaust. Fitted after the filter in the air preparation unit.

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Lubricator

Square on its corner with a short line from the top corner, for the device that adds oil mist to the air stream. Only needed where the connected components require lubricated air.

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FRL unit, simplified

Single rectangle combining filter, regulator with gauge and lubricator, with the condensate drain below. Use it in machine diagrams where the air preparation unit does not need to be shown in detail.

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Silencer

Rectangle with internal baffles and an exhaust triangle, fitted to a valve exhaust port to reduce noise. Hangs from the port it serves.

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Exhaust port

Open triangle pointing away from the valve, for a port that vents directly to atmosphere without a connection. Attach it below exhaust ports 3 and 5.

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3/2 directional control valve

Three-port, two-position valve shown normally closed: at rest port 2 exhausts to 3 and supply 1 is blocked, when actuated 1 feeds 2. Used for single-acting cylinders and signal generation.

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5/2 directional control valve

Five-port, two-position valve with two outputs and two exhausts; supply 1 switches between outputs 2 and 4. The standard valve for double-acting pneumatic cylinders.

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5/3 directional control valve, closed centre

Three-position valve whose centre position blocks all five ports, trapping air in both cylinder chambers. Used to stop a cylinder in mid-stroke.

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Push-button actuator

Manual operation by a push button, drawn as the operating stem capped with a rounded head. Usually paired with a return spring.

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Roller actuator

Mechanical operation by a roller on the end of the plunger, drawn as a circle with a centre dot. Used for limit valves that a moving cam or machine part actuates.

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Solenoid with pilot actuation

Solenoid that switches an internal pilot stage, which then shifts the main valve with air pressure, drawn as the coil next to a box with an open triangle. The usual operator on solenoid valves for larger flows.

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Return spring

Zigzag spring that returns the valve to its rest position. Drawn for the right-hand side of the valve; mirror it for the left.

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Single-acting cylinder, spring return

Cylinder with one supply port and a spring that retracts the piston when the air is exhausted. Used for short strokes such as clamping and ejecting.

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Double-acting cylinder

Cylinder with a port at each end, so compressed air both extends and retracts the rod. The most common pneumatic linear actuator.

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Double-acting cylinder, adjustable cushioning

Double-acting cylinder with cushioning on both sides of the piston, the oblique arrows showing that the cushioning is adjustable. It slows the piston near the end of stroke to reduce impact.

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Check valve

Ball against a seat that lets air pass from left to right and blocks the reverse direction. Used to hold pressure in a branch or keep flow one-way.

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One-way flow control valve

Adjustable throttle with a check valve in parallel, restricting flow in one direction only. Fitted at cylinder ports to set the piston speed, usually by throttling the exhaust air.

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Quick exhaust valve

Ball valve that feeds the outlet from the inlet and, when the inlet drops, vents the outlet straight to atmosphere. Mounted close to a cylinder port to increase piston speed.

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Shuttle valve (OR)

Valve with two inlets and one outlet in which a single ball closes the inlet with the lower pressure. Gives an OR function, for example to operate a cylinder from two different points.

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Two-pressure valve (AND)

Valve with two inlets and one outlet that passes a signal only when both inlets are pressurised. Used for AND logic such as two-hand safety controls.

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Pressure gauge

Measuring instrument circle with an oblique pointer arrow, connected to the line whose pressure it displays. Typically drawn at the regulator outlet.

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Vacuum generator (ejector)

Ejector in which supply air flows through a nozzle and creates vacuum at the side port, with the air exhausting on the right. Used to feed vacuum cups for handling parts.

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